Figure 1

The Wind River Range in Wyoming is captured by Spot 5 on Aug. 29, 2007. This image was used with others by Dr. Pelto to study glacier melt in the area. Image courtesy of Spot Image.

Figure 2

Milk Lake Glacier has completely disappeared from 1984 to 2009.

Figure 3

Ice Worm Glacier is disappearing; it has lost all of its snow cover in six of the last 10 years. The top is retreating as fast as the bottom.

Figure 4

This is the accumulation zone of the Columbia Glacier from the headwall. Notice the number of annual horizons exposed on August 1, 2005. This is the third consecutive year of significant negative annual balances, and follows 2004 when the AAR dropped below 20.

Figure 5

Foss Glacier, North Cascades, in 1988 and 2005 indicating the change in the extent of the glacier. Visible are substantial marginal retreat in the accumulation zone and new rock outcroppings in the accumulation zone.

Alpine glaciers worldwide are retreating, and some will disappear in coming decades. Because the behavior of glaciers results directly from local weather conditions, they are considered reliable gauges of climate change and are undergoing intense scrutiny. Often lost in the midst of this scientific examination is the fact that glaciers also serve practical purposes. They are vital sources of fresh water, and their disappearance can have devastating local economic and environmental effects.

Dr. Mauri Pelto, a geologist and glaciology professor in the Environmental Sciences Department at Nichols College in Dudley, Mass., has studied alpine glaciers throughout the world for 26 years. After watching the slow retreat and eventual disappearance of several glaciers, Pelto recognized that significant societal value could be gained by devising a method to forecast which glaciers are holding their own and which are heading toward extinction.

Pelto believes that satellite imagery holds the key to accurately predicting the futures of alpine glaciers and could ultimately serve as the centerpiece of automated forecasting techniques. In 2008, Pelto applied for and received assistance in the form of satellite imagery from Planet Action, a climate research initiative of Spot Image in partnership with ESRI. Early results of his project indicate the glaciologist has developed an entirely new means of monitoring glaciers and interpreting their reaction to climate change.

“We felt that Dr. Pelto’s research was at the cutting edge of developing a practical, automated mechanism for monitoring glacial disappearance worldwide,” said Antoine de Chassy, President of Spot Image Corp.

Weather Impacts Glaciers

Part of the impetus for Pelto’s desire to establish a scientifically based forecasting mechanism has been the well-publicized, yet erroneous, predictions of glacial demise across large geographic regions. Exaggerated reports on the imminent deaths of all glaciers in the Himalayas and Glacier National Park over the next 15-25 years are two examples.

“They are not going to disappear by the year 2035,” said Pelto. “Some glaciers are doing just fine there…they aren’t growing, but they are shrinking very slowly, while others are shrinking very fast.”

Confusion over the fate of glaciers in a given area stems from a misunderstanding of the complexity of these dynamic geologic features. A single mountain range may contain hundreds of glaciers, and it is tempting to assume that localized weather and climatic conditions are influencing them all identically. But in reality, different internal factors, such as the altitude of the snow accumulation zone, are at work in different glaciers. One glacier may be retreating, while another immediately adjacent to it is stable.

“Glaciers right next to each other are doing different things,” said Pelto, noting that one glacier’s shrinkage and potential disappearance is no indication that its neighbors are in trouble.

The value of monitoring both alpine and continental ice sheets as part of climate change research is indisputable. The behavior of glaciers over the course of a year depends largely on one external factor – the weather. As climate indicators, glaciers are quite different from other proxies for measuring historic temperature. Tree rings and coral reefs, for instance, can be impacted by many outside variables aside from weather and are therefore less reliable climate indicators.

“There is nothing else that matters to the glacier (besides climate),” said Pelto.

The status of a glacier is typically measured by its mass balance, a ratio of the new snow accumulated over the winter versus the snow that melted during the summer. A positive mass balance means there has been a net increase in snow over the year, and the glacier is growing or advancing. But a net loss of snow indicates the ice sheet is thinning or retreating. Glaciers can go through many periods of advance and retreat over the course of their existence.

Glaciologists like Pelto can calculate the mass balance of individual glaciers by measuring their snow pack every year. They can also make historical estimates of snow pack changes by measuring the thickness of annual ice layers found in the stratigraphy of deep glacial crevasses, in much the same way foresters measure the thickness of tree rings.

Assessing mass balance on an annual basis is the best way to track the current status of the glacier – whether it is stable, retreating or advancing. However, the problem with mass balance calculation is that it requires onsite observations and measurements of the snow pack. More importantly, because glaciers are inherently difficult and dangerous to visit in person, only a limited number of glaciers can be actively monitored at one time.

Monitoring Glacial Change

Pelto concluded that for glacial monitoring to have significant value for either climate change research or fresh water supply assessment, glaciers have to be monitored individually. Given the fact that hundreds of thousands of glaciers are carving the Earth’s surface at any given time, this seemed like an impossible chore. But Pelto began experimenting with other means of measuring glacial conditions.

On visits to glaciers around the world, the scientist began photographing the snow lines of specific glaciers repeatedly at the same time of year. He photographed or directly measured the elevations of the snow line on the glaciers at their tops, bottoms, and at other land marks in between. He tried pinpointing the snow lines in 30-meter resolution Landsat imagery but found it too coarse for accurate measurement on smaller alpine glaciers. In-person visits were still the best method of collecting data.

In the course of his studies, spanning two and a half decades, Pelto discovered that the conventional method of assessing glacial disappearance was incorrect. First-year geology students are taught that alpine glacial activity, and therefore its health, is best monitored at its leading edge, or terminus. If a glacier suffers from a net loss in mass, its lower terminus will begin to recede back up the mountain from one year to the next.

While this observation is true, a receding glacier is not necessarily a disappearing one, Pelto realized. In fact, the speed of recession at the lower edge has little bearing on whether the entire ice mass will disappear completely, and some that lose ground at the lower terminus one year may gain it the next. The real sign that a glacier is in jeopardy is found at its upper reaches, known as the accumulation zone.

“Glaciers that were disappearing were retreating at the top, not just at the bottom,” said Pelto, noting that a mass balance number just can’t reflect this situation.

A constant recharge of snow into the accumulation zone is crucial for its survival. If there isn’t enough new snowfall over the accumulation zone during the winter or if too much snow consistently melts from that upper-most area during the summer, the glacier has crossed a critical threshold and is usually doomed to disappearance. This absence of snow or increase in melt rate can be caused by long-term warming in temperatures.

Planet Action Fills the Data Gap

Once a glacier had disappeared, the researcher reviewed his field notes, photos and measurements and saw the telltale signs of accumulation zone losses exhibiting themselves years before. One of the most visible signs was the emergence of rock outcrops in the upper parts of the glacier. The other was the retreat of the glacier perimeter in the accumulation zone. “You could see that in Spot satellite imagery,” said Pelto. He explained that once bedrock peeks through the ice sheet, the heat balance changes irreversibly because the rocks absorb so much thermal radiation from the sun.

Since 2007, the Planet Action program initiated by Spot Image has put satellite imagery into the hands of scientists and students working on projects studying the impacts of climate change. After submitting a proposal, Pelto received pairs of Spot images acquired during different years over parts of the North Cascade Mountains in Washington and the Wind River Range in Wyoming. Each image included about 30 glaciers in areas he had been studying. See Figure 1.

The images had been acquired by the Spot 4 and 5 satellites, which collect both panchromatic and multispectral data. Working in ArcGIS, Pelto found that viewing imagery datasets comprised of visible and near-infrared bands at 10-20 meter spatial resolution had the best combination of regional coverage and feature detail. For some glaciers, these images clearly showed the presence of rock outcrops that had not been visible in images from just a few years before.

Pelto also used the GIS software to manually draw perimeter lines around the margins of the glaciers in the imagery. By overlaying these perimeters on USGS topographic maps, he recorded the separation of the lines from one year to the next.

As expected, the Spot imagery enabled Pelto to identify the two key indicators of future glacier disappearance – emerging rock outcrops and falling snow line elevation in the accumulation zone. In the Northern Cascades and Wind River Range, the research indicated that two-thirds of glaciers in the study areas are disappearing and will not survive the current warming period. The other third represents a consistent accumulation zone with no apparent changes. See Figures 2-5.

Automating the Process

“With some glaciers disappearing in the study areas and others remaining stable, Dr. Pelto’s Planet Action project confirmed the importance of monitoring the ice masses individually,” said Spot Image’s de Chassy. It also verified that disappearance indicators can be found in multi-temporal Spot scenes.

Pelto says the next step is to automate the glacier monitoring process. Automated change detection algorithms can be written to continually monitor Spot scenes over mountainous regions to pinpoint emerging outcrops and thinning upper margins. Once enough disappearing glaciers have been studied, scientists will be able not only to identify those with no future, but also to forecast how long until they’re gone. This will be a crucial advantage for areas that depend on glaciers for fresh water.

“For glacier disappearance, we’ll make water management decisions 20-30 years out,” said Pelto.

Currently, temperate alpine glaciers in the Andes, European Alps, Himalayas, Norway, Iceland, Western Canada and the U.S. Pacific Northwest supply fresh water to drainage basins at lower elevations. In these areas, glaciers provide vital summer run-off that supplies up to 30 percent of river water upon which fish hatcheries, agricultural irrigation, hydroelectric power plants and drinking water reservoirs depend.

Knowing a decade or more in advance that a third of the water supply will disappear will give these areas significant advantages to take management steps that will minimize the impact on the local economy. “Loss of glaciers can be forecasted accurately and inexpensively with automated change detection methods and Spot satellite imagery,” concluded Pelto. This prediction can be accomplished with routine GIS algorithms using multi-temporal imagery as inputs.